THERMO-MECHANICAL TESTS ON TRACKER LADDERS (Low temperature problem on plane 1) Status Report: D.Rapin Sept 26,2012 (help from Giovanni, Franck, Mingming,...) GOALS: Verification of ladder integrity in case of many low temperature excursions. If possible a better understanding of behavior of ladder mechanics and geometry with temperature. FACTS: Ladders were built at ~ +20°C For ladders close to the center of plane 1, an almost constant temperature gradient of ~23 ° C is present between hottest part of the ladder (hybrid) and the coldest part (last wafer) Four cold periods per year (Four cold excursions per year). Temperature of coldest wafers in plane 1 ranges between -3 ° C and -15 ° C. Temperature of front-end hybrids is above 5°C. in normal operation !

Ladder components Flexibility

Thermo-elastic calculations showed that the critical problem may be the shear stresses applied to the glue (Araldit 2011,no post curing) which bonds the Upilex (Kapton) cable and the Silicon wafers together. It is due to the different thermal expansion of the two materials. Two experimental studies: Study of mechanical integrity ( Look for possible mechanical damages) (Geometry vs temperature not yet started ) Reinforcement and fixation on support plane

STUDY OF MECHANICAL INTEGRITY of the wafer assembly part of ladders Significant damages on ladder are detected through: Displacement of components. Weakness of assembly ( displacement of components after application of a reasonable force. ) Weakness of micro-bonds ( not expected ) 60 thermal cycles simulating 15 years of thermal stresses: First 0 to -20 deg ( slightly worse than present situation ) Then +5 to -30 deg...if previous test... And +10 to -40 deg... is successful. Tests and measurements on ladders: 3D Metrology (optics) and visual tests ( integrity of the legs gluing ) Peeling test: Pull-out with a 2 Newton force (100 time the weight of one wafer) on each corner of each wafer. Read-out of strain gauges during cycling. A crack in the structure will produce a sudden change of the constraints. Will also provide a verification of model. Micro-bonds quality (force needed to break it)

STUDY OF MECHANICAL INTEGRITY Material for the tests: A mock-up of a portion of plane1 with fixations for 11- or 12-wafers ladders was built by RWTH Aachen. Ladders available for tests with 11 or 12 wafers: UniGe: Mech.Proto, Flight:L11GI007, ExhibitionLadder, Two AMS01 ladders Perugia: 1 AMS02 with legs, 5 AMS02 without legs (feet). Only few ladders available  Extract the maximum of information from the tests. Read-out equipment for strain gauges (provided by Perugia). A climate chamber (dry air) is available at UniGe (used by ATLAS). Lab, workshop and 3D optical metrology (MicroVu) available at UniGe. Logistics  Tests made at DPNC-UniGe (... then at Terni if vacuum mandatory) Sequence of tests: Metrology / 60 thermal cycles/ Metrology and comparison Pull-out test / Metrology and comparison If no apparent damages, repeat with more severe temperature limits. Performed on 2 ladders: Mech.Proto, Flight:L11GI007

Honeycomb support plane with inserts (Aachen) 11-wafer mechanical prototype mounted (L0)

L11GI007 flight ladder (L1) on honeycomb in climate chamber

UniGe climate chamber ~1 m to 180 deg (used by ATLAS) Perugia strain gauges read-out equipment. Software prepared by Giovanni Ambrosi.

Example of cycling

Suction cup for the pull-out test on each corner of each wafer 2 Newton force (100 times one wafer weight) Mechanical proto L11GI007 flight ladder

Learning how to use the MicroVu 3D optical measuring machine

Testing the quality of the micro bonds: wafer to wafer wafer to Upilex cable ~ 10 gf are needed to break the bonds

Example of micro-bond test result

The 3 coordinates of the four crosses of each wafer are measured. Machine range limits to ~8 wafers:  two measurements for one ladder  Translation+rotation to adjust the two measurements on their common part. Resulting combined measurement is compared with the ideal ladder. or Two combined measurements can be compared to detect changes.

Example: mechanical prototype ladder (L0)

Z inserts not corrected

Test of FEA Model (F.Cadoux) 150 gr weight 27 µ

29 µ Verification with Mechanical prototype Positions of LEGS

Results of L11GI007 (L1) flight ladder test

post -30deg

Deltas after -40deg cycles

Post -40deg Delta after pull (upper part)

Push test

SUMMARY & CONCLUSION Two ladders tested (1 mech.proto, 1 flight ) 60 cycles = 4 [cycle/year] x 15 years (-20, -30, -40) Up to now, no mechanical integrity problems have been seen (geometry, solidity, micro-bonds) by D.R. Electrical behavior (specially FE hybrids) not tested Geometry.vs. Temperature not tested yet Strain gauges study still in progress

spare slides

First estimate on Ladder temperature for one ladder in plane 1 -18°C on the worst silicon wafer! Emissivity are different on both sides: -20 °C max to the Tracker support, em.=0.9 0°C to the TRD top side, em.=0.1 Preliminary Franck Cadoux december 2011

First estimate on Ladder deflection: -20°C (homogeneous) Uvert.= -74 microns Ulong.= -94 microns Preliminary depends on thickness and surface of glue 140 microns

First estimate on mechanical -20°C No issue / silicon (7 Mpa) Preliminary

First estimate on mechanical -20°C glue joint: 18 MPa (VMises; peak value) Shear glue joint: 10 MPa (peak value) Epoxy shear strength is given at 10Mpa (without post curing operation!) Preliminary depends on the amount of glue